[Role of thymine dimers in the UV mutagenesis of bacteriophage sd].

The sensitized irradiation (lambda greater than 310 nm) with AcphiM induces plaque mutants of extracellular phage Sd. Thus, TT in phage Sd DNA are both lethal and mutagenic. The yield of plaque mutants is about 3-fold lower as compared with the yield after UV-irradiation (lambda = 254 nm). The theoretical analysis of UV-induced mutagenesis curves of phage Sd was carried out. It is concluded that the following photoproducts make a contribution in the mutagenic effect of near-UV (lambda = 254 nm): 1) lethal pyrimidine dimers; 2) other lethal photolesions; and 3) non-lethal mutagenic photoproducts of cytosine. The cytosine photohydrate contribution nearly twice exceeds the total contribution of lethal photoproducts. It is assumed that bacteriophages T4 and Sd have their own system of repair, like SOS-repair in bacteria.